It was an only-in-San-Diego kind of moment: On a loading dock outside the federal fishery lab in La Jolla, two giant disc-shaped opah — some of the ocean’s more captivating creatures — lay frozen and shining in the morning sun.

Researcher Owyn Snodgrass poured water on the stiff fish, melting a thin layer of ice and revealing orange-pink hues and silver spots. After showing a few passers-by, he lugged the 100-pounders back into a storage freezer for safekeeping next to a mako shark and other frozen figures destined for various studies.

Eventually, Snodgrass and his colleagues at the Southwest Fisheries Science Center will thaw the opah and dissect them as part of a low-budget effort to better understand a species that has been showing up far more often in the nearshore waters of Southern California over the past few years.

Opah — also called moonfish — typically have been found in tropical and temperate oceans, and thousands have been caught in Hawaii by longline fishermen targeting bigeye tuna.

But it appears that the opah population is growing or the fish are expanding their range into the eastern Pacific Ocean, likely driven by some unknown combination of changing ocean conditions, and Snodgrass is among a handful of local scientists determined to learn more.

“We know almost nothing about their biology,” said Snodgrass, as a colleague slit open a forearm-sized opah stomach and removed a few small squid from inside.

“But they seem to be gaining more attention as a consumable product. It would be good to learn more about their biology at the same time — before there becomes this incredible demand.”

Because opah aren’t targeted by commercial fisheries, there has been little concern about the fate of the population. That means there’s little research money and little scientific exploration. There also are no current regulations with regard to catching them, which is a relatively rare occurrence given that they spend much of their time far below the surface.

“It’s the fish of a lifetime,” Snodgrass said. “It’s like winning the lottery. Nobody is expecting one of these. They are just doing something different to try to get a bite and they hook an opah.”

Regardless of their rarity or the lack of research, opah have something of a cult following partly because of their tasty meat and partly because of their odd appearance.

“My biggest dream is getting an opah underwater shot,” said Jon Schwartz, a marine photographer and schoolteacher who lives in North County.

In 2010, a friend of his saw an unusual manhole-sized object wash ashore in Leucadia. “Lo and behold, it was an opah — maybe 100 pounds or something — and it was in perfect condition,” Schwartz recalled.

He hasn’t seen one in local waters since that time, but he remains hooked.

“It looks just like a toy, but it’s a giant fish,” Schwartz said. “I don’t see how you could not be fascinated. It doesn’t look like something that can swim.”

Back at the fisheries lab, Snodgrass became curious about opah a few years ago, when they started popping up regularly on federal marine research trawls in the region after being absent for the previous 10 or 15 years.